1. Field of the Invention
This invention relates to a device for automatically feeding original documents one by one to an image processing device such as a copying machine, and more particularly to a document feeding device capable of consecutively feeding duplex documents set on a supply tray in order of page to the image processing device and discharging, to a discharge tray, the documents in the same order of page as that of the documents initially set on the supply tray.
2. Description of the Prior Art
A variety of document feeding devices have been widely applied to image processing devices of various types such as a copying machine, image scanner and facsimile in order for automatically feeding one or more original documents to the image processing devices. However, there have so far been no document feeding device available for rationally handling a double-sided printed original document having images to be read on both sides thereof with good efficiency, which document will be simply referred to as "duplex document" hereinafter.
Generally, for reading the images on both sides of the duplex original document, document transporting means capable of turning over the duplex document in the document feeding device is required, but it is difficult to turn over and transport the document at high speed with high efficiency by use of a simple mechanism.
Japanese Patent Application Publication HEI 8-133551(A) discloses one example of a conventional document feeding device having a function of turning over a duplex document for reading images on both sides of the document by use of a single reading means.
The known document feeding device disclosed in the publication comprises a document supply part 1 for sending out one or more original documents dn (n=1,2,3, . . . ) to be image-processed one by one, a document transport part 2 including a forwarding roller 2a around which a document transport passage R is formed, a switchback part 3 disposed at a document exit so as to send the document back to the transport part 2 to turn the document over, and a document discharge part 4 having a discharge tray 4a to which the document is sent out through the switchback part 3 after being image processed, as shown in FIG. 1(A).
The document supply part 1 includes a document supply tray 1a on which the documents dn to be image-processed are stacked with the image surface upward, and document forwarding means 1b for sending out the documents stacked on the supply tray 1a one by one.
The switchback part 3 includes reversible rotating rollers 3a for switching back the document from the transport passage R to the transport passage R or discharging the document to the discharge tray 4a.
The aforementioned document feeding device is generally attached to an image reading portion of the image processing device M such as a copying machine in such a state that the forwarding roller 2a is opposite to image reading or scanning means C composed of a linear array CCD photoelectric element or the like mounted in the image processing device M.
When a single-sided printed document having an image to be read on one side thereof is given, the document d1 is transported along the passage R from the supply tray 1a to the discharge tray 4a through the image reading point X as shown by the dotted line in FIG. 1(A). When the document passes over the image reading means C located at an image reading point X, the image on the document is read by the image reading means C, and then, the document is sent out to the discharge tray 4a with the image surface downward. The following documents d2, d3, . . . are successively handled in the same manner as above and sent out onto the top of the document d1 which has already been discharged onto the discharge tray 4a. Thus, the documents finally placed on the discharge tray 4a are piled in the same order of page as that in the documents initially set on the supply tray 1a.
In a case that the given documents has images to be read on the odd-numbered and even-numbered pages thereof, i.e. duplex documents, the document must be turned over after the images on both sides of the document are read by the image reading means C, and then, sent out to the discharge tray 4a with the odd-numbered page facing downward, as shown in FIG. 1(B). That is, the uppermost of the duplex documents is first sent into the document passage R (a1), forwarded through the image reading point X with the odd-numbered page facing the image reading means C so as to read the image on the odd-numbered page by using the image reading means C (a2), and sent into the switchback part 3 (a3). The document introduced into the switchback part 3 is sent back into the document passage R by reversing the rollers 3a (a4).
The document forwarded along the document passage R travels around the forwarding roller 2a (a5) and again forwarded through the image reading point X with the even-numbered page facing the image reading means C so as to read the image on the even-numbered page by using the image reading means C (a6), and then, it is sent into the switchback part 3 (a7). If the document sent into the switchback part 3 after reading the images on both sides thereof is direct sent out to the discharge tray 4a, the odd-numbered page of the document faces upward, as a result of which the first document d1 and following documents d2, d3, . . . which are finally piled on the discharge tray 4a are not in the same order of pages as that of the documents initially set on the supply tray 1a.
Therefore, the document sent into the switchback part 3 upon completion of reading the images on both sides of the document is sent back to the document passage R once more, made circulate about the forwarding roller 2a to be turned upside down (a8), and then, sent out to the discharge tray 4a through the switchback part 3 (a9). Consequently, the document finally lying on the discharge tray 4a has the odd-numbered page facing downward, and the following documents are discharged in the same order of page as that of them initially set on the supply tray 1a.
Thus, in order to finally take the duplex documents out from the discharge tray 4a in the same order of page as that of them initially set on the supply tray 1a, the documents must travel at least three rounds of the document passage R around the forwarding roller, resulting in decrease in operation speed and efficiency of the document feeding device.
Furthermore, the circumference of the forwarding roller 2a in the aforenoted conventional device must be made equal to or larger than the length of the maximum document which is permitted to be handled by the document feeding device so as to prevent the front end and rear end of the document, which possibly move in the opposite directions in the switchback part 3, from coexisting in the switchback part 3 when the document is sent into the switchback part 3 and returned to the transport passage R around the roller 2a. Thus, the forwarding roller 2a cannot be made small in diameter, entailing difficulty in making the document feeding device compact.